The deposition of organic contaminants (i.e., pitch and stickies) on surfaces in the papermaking process is well known to be detrimental to both product quality and the efficiency of the papermaking process. Some contaminating components occur naturally in wood and are released during various pulping and papermaking processes. Two specific manifestations of this problem are referred to as pitch (primarily natural resins) and stickies (synthetic contaminants from recycled paper). Pitch and stickies have the potential to cause problems with deposition, quality, and efficiency in the process as mentioned above.
The term “pitch” can be used to refer to deposits composed of organic constituents which may originate from these natural resins, their salts, as well as coating binders, sizing agents, and defoaming chemicals which may be found in the pulp. In addition, pitch deposits frequently contain inorganic components such as calcium carbonate, talc, clays, titanium and related materials.
“Stickies” is a term that has been increasingly used to describe deposits that occur in the systems using recycled fiber. These deposits often contain the same materials found in “pitch” deposits in addition to adhesives, hot melts, waxes, coatings, and inks.
The deposition of organic contaminants, such as pitch and stickies, can be detrimental to the efficiency of a pulp or paper mill causing both reduced quality and reduced operating efficiency. Organic contaminants can deposit on process equipment in papermaking systems resulting in operational difficulties in the systems. The deposition of organic contaminants on consistency regulators and other instrument probes can render these components useless. Deposits on screens can reduce throughput and upset operation of the system. This deposition can occur not only on metal surfaces in the system, but also on plastic and synthetic surfaces such as machine wires, felts, foils, Uhle boxes and head box components.
From a physical standpoint, “pitch” deposits have usually formed from microscopic particles of adhesive material (natural or man-made) in the stock which accumulate on papermaking or pulping equipment. These deposits can readily be found on stock chest walls, paper machine foils, Uhle boxes, paper machine wires, wet press felts, dryer felts, dryer cans, and calendar stacks. The difficulties related to these deposits included direct interference with the efficiency of the contaminated surface, therefore, reduced production, as well as holes, dirt, and other sheet defects that reduce the quality and usefulness of the paper for operations that follow like coating, converting or printing.
From a physical standpoint, “stickies” have usually been particles in the stock which originate from the recycled fiber. These deposits tend to accumulate on many of the same surfaces that “pitch” can be found on and causes many of the same difficulties that “pitch” can cause. The most severe “stickies” related deposits however tend to be found on paper machine wires, wet felts, dryer felts and dryer cans.
Historically, the subsets of the organic deposit problems, “pitch” and “stickies”, have manifested themselves separately, differently and have been treated distinctly and separately. This was true because mills usually used only virgin fiber or only recycled fiber. Often very different treatment chemicals and strategies were used to control these separate problems. However, current trends are for increased mandatory use of recycled fiber in all systems. This results in a co-occurrence of stickies and pitch problems in a given mill.
Methods of preventing the build-up of deposits on the pulp and paper mill equipment and surfaces are of great importance to the industry. The paper machines could be shut down for cleaning, but ceasing operation for cleaning is undesirable because of the consequential loss of productivity, poor quality of the paper while the machine is partially contaminated and “dirt” which occurs when deposits break off and become incorporated in the sheet. Preventing deposition is thus greatly preferred where it can be effectively practiced.
One of methods to prevent pitch/stickies contaminants to deposit on papermaking equipment surfaces is to add various process aids into pulp slurry that contains pitch/stickies contaminants. For examples, a dispersant is added to pulp suspension to disperse and stabilize the contaminant particles, thus keeping them from deposition; or a detackifier is added to pulp suspension to render the contaminant particles less stickier, thus, less depositable; or a cationic polymer is added to pulp suspension to fix the contaminant particles onto fibers' surfaces, thus, removing them from the systems.
Another method to prevent pitch/stickies contaminants to deposit on papermaking equipment surfaces is to spray a deposit inhibitor on the papermaking equipment surfaces. Various deposit inhibitors have been invented to spray on surfaces of papermaking felts, forming wire, and press rolls. These deposit inhibitors either form a protective layer on the surfaces or change chemical properties of the papermaking equipment surfaces and make the surfaces less prone to the deposition of pitch/stickies contaminants.
U.S. Pat. No. 4,710,267 disclosed a process of reducing stickies contaminants in secondary fibers by adding a tertiary amine or quaternary ammonium cationic surfactant to the pulp after deinking but before sheet formation. U.S. Pat. No. 4,190,491 disclosed a process for preventing deposition of pitch by adding in a pulp suspension a cationic polymer derived from ethylenically unsaturated monomers. U.S. Pat. No. 4,765,867 disclosed to control pitch deposition by adding the pulp a quaternized polyamine ionene polymer. The polymer is derived from the condensation polymerization of epichlorohydrin with a dialkylamine. U.S. Pat. Nos. 5,223,097 and 5,626,720 disclosed to spray papermaking wires a quaternary polyamine which is a reaction product between an epichlorohydrin (EPI) and a dialkylamine.
U.S. Pat. No. 4,995,944 disclosed to apply papermaking felts a mixture of cationic polymer and a cationic surfactant. The cationic polymer is a dicyandiamide formaldehyde condensate polymer. U.S. Pat. Nos. 5,246,548 and 5,300,194 disclosed to apply a cationic polymer and a water dispersible anionic aromatic polymer to papermaking dryer fabrics. U.S. Pat. No. 5,368,694 disclosed to apply the paper machine equipment surface a cationic polymer or a cationic surfactant while adding an anionic polymer or an anionic surfactant into pulp suspension to maintain an anionic charge in the suspension.
U.S. Pat. No. 4,956,051 disclosed to use a partially hydrolyzed polyvinyl alcohol to spray on the felts, wire, and press rolls of papermaking equipment. U.S. Pat. Nos. 5,723,021 and 5,952,394 disclosed to use a composition comprising a partially hydrolyzed polyvinyl alcohol, a gelatin, and a cationic polymer. The cationic polymer is a polyamine, a polyethyleneimine, or a copolymer of acrylamide and an ethylenically unsaturated amine
U.S. Pat. No. 6,517,682 disclosed to apply a cationic polymer and a nonionic surfactant to papermaking felts. U.S. Pat. No. 7,534,324 disclosed to apply papermaking felts or equipment surface a nonionic polyoxyalkylene surfactant in which the polyoxyalkylene chains contain repeating units of both ethylene oxide (EO) and of a higher alkylene oxide (AO).
US patent application 2008/0029231 disclosed to apply papermaking systems including the surfaces of papermaking equipment a hydrophobically modified polyethylene glycol).